Ka band propagation experiments on the Australian low earth orbit microsatellite 'FedSat'
- Publication Type:
- Thesis
- Issue Date:
- 2008
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The emergence of the 20/30 GHz Ka band in satellite communications in recent
decades has seen systems designers faced with the problem of severe signal
attenuation though atmospheric effects, especially rain. Previous experimental
missions, such as ACTS and OLYMPUS, have succeeded in collecting large
amounts of propagation data, which has led to the development of various
semi-empirical models for link design. However, all these experiments were
carried out over geostationary satellites, and with a recent tendency towards
constellations of low-earth orbit satellites for true global coverage and increased
system capacity for real-time services, these models are in need of adaptation
for variable elevation angles and the effects of rapid satellite movement.
The work contained in this largely experimental thesis presents the Australian
‘FedSat’ LEO microsatellite, carrying a Ka band beacon and a bent-pipe mode
transponder, as an ideal research platform for such investigations. The inhouse
design, deployment and operation of a very low-cost, fast-tracking earth
station is examined in-depth, and particular attention is paid to systems design
aspects involving numerous hardware and software technologies, which interact
with each other in a highly complex manner, for example Doppler frequency
tracking, pointing accuracy control and precise signal power measurements.
Prior to and during the operational phase, several crucial design improvements
are discussed, implemented and verified. Successful and reliable tracking by
using pointing coordinates derived from two-line elements, as opposed to GPS
data, is experimentally proven.
The design of the earth station prototype is validated by the collection of
Ka band propagation data in both beacon and bent pipe modes. After postprocessing
of the data, attenuation results for various weather conditions and
down to elevation angles well below 10 degrees are illustrated and interpreted in conjunction
with the prevailing weather conditions. While a comparison with the
measurements from geostationary satellites widely confirms the validity of the
results, other interesting phenomena are unveiled that require further investigation.
In particular, the extent of low-angle scintillation appears to be wider
band than previously reported in published literature, which is a potentially
important finding.
Finally, the experience gathered during the late-stage design and the operation
of the earth station gives rise to several recommendations for further design
improvements and operational strategies, which may be helpful for future research
groups in this field wishing to conduct similar LEO Ka band propagation
experiments on a low budget.
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